Approximations:

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rattus

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It is a decided advantage in technical work to know when approximations are in order. For example, in the post "Code Theory Question", with a parallel combination of 20K and 0.0135 Ohms and 200A current. The lower resistance determines the voltage drop of 2.7V which causes a current of 135 micorAmps through the 20K. The

This raises the question of the difference in precision and accuracy. This in turn brings up the question of significant figures. For example, just because your calculator or DVM reads out to six figures, that does not mean all six figures are meaningful.

I will leave it to the membership to discuss this item at length--I hope.
 
Re: Approximations:

Like Charlie B., I too have some sayings. But this one I took from someone slse.

Precise approximation.

Take all the data and all the measurements and do all the math. But when you're doing something statistical or using averages or approximating.

Although you can have 50 decimal places of precision in the final number, the tolerance may be 20%.
 
Re: Approximations:

Sorry, rattus. I see no value in this. Everything in the NEC is essentially an approximation. I know the difference between accuracy and precision. I also know it will not help anyone decide whether to use a #8 or a #6 wire.

Please ask a question or present an issue.
 
Re: Approximations:

Charlie B, I am sure that many of the members understand precision, accuracy, and approximations, but some do not. I thought it would be a meaningful topic. If you think otherwise, I will not be offended if you delete it.
 
Re: Approximations:

Rattus, this thread will not be deleted. Charlie was just trying to make the point that most of the Code requirements are indeed approximations so the accurate calculations are generally approximations in themselves.

Look at the conduit fill percentages, the derating charts, the ampacity charts, etc., they are all approximations. A lot of times we accept a proposal and then more data is presented on the next cycle or so to make changes. These tables are also open for interpretation by different AHJs. Of course, solid engineer calculations will permit installations that would normally be Code violations. :D
 
Re: Approximations:

Charlie, I understand what is being said about the approximate nature of the code, but surely there are times when one puts the book away and pulls out his calculator. Then one must consider the accuracy and precision of the numbers. Or, for no other reason, an understanding of these concepts helps one to be the complete electrician.

The reason I posted this is that I noticed some members making a difficult problem out of a simple problem in another post and thought that this would be appropriate.
 
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